A visually induced illusion of body tilt in a horizontal plane

Unexpected spontaneous reports of an illusion of body orientation have been observed in previous studies on the effects of a tilted overhead frame on supine observers. The present studies were designed in an attempt to describe and measure this illusion. The findings suggest that when objectively aligned with invisible side walls of the room, some subjects may experience an illusion that they are tilted in a horizontal plane with respect to the room walls in the direction opposite to frame tilt from the longitudinal body axes. The results are discussed in terms of a model of visual-vestibular interactions.